Characterization of PAMBE grown TiN/AlN/TiN Josephson junctions

In the pursuit of epitaxially grown Josephson Junction (JJ) creation, this work investigates the growth of TiN//AlN//TiN tri-layer heterostructures. This material stack offers several benefits over traditional Al//AlO_x//Al JJs. These include enhanced mechanical stability, potentially reduced two level system loss (TLS) due to the use a crystalline AlN barrier, and heightened superconducting critical temperature, which may reduce the number of thermally excited quasiparticles. This work will be presented in two parts: here, the device fabrication and electrical characteristics of JJ devices are presented, while materials development and growth of the tri-layer structure were covered before in a separate presentation.

Devices were defined using a two-step ICP dry etch that created a vertical mesa JJ and connected lower TiN contact pad.  A SiN_x dielectric layer and Al top contact layer completed the device.  Initial cryogenic DC-IV characterization measured a critical current density larger than 5 kA/cm², for a 4-nm-thick AlN tunnel barrier.  This result is significantly higher than reported AlO_x and AlN junctions. To further characterize this heterostructure design, the critical current density dependance on thickness and area will be discussed.